Seamus Haley

The important thing to remember with LD50s is that they need to be looked at in the context which they were performed under and that the results have a limited meaning.

I got into an enormous argument with a few people in an online chat about this a few months back and am still a bit hot under the collar over it, so the rest of this is going to be something of a rant...

Different snakes have different venom compositions... both between species and between individuals. The venom types for species can often be generalized into broader catagories or even slightly more specific toxic compounds found within the venom, but the individual snakes have venom that will differ slightly in it's exact composition based on the reccent diet of the animal, the environmental conditions, the animal's age, the current hormonal levels, when it last envenomated a prey item or was milked... All very slight differences, but when looking at tests that use the venom from multiple milked individuals and venom that may or may not be "fresh" when it's applied (much like any other mostly organic substance, venom changes chemically as it ages) and when given in amounts that often vary by a milligram or two for each test group... It becomes a serious issue area of concern when looking at the results and the potential for uncontrolled factors in the experiment.

The different venom types (broad catagories) also react differently to different kinds of tissue... pretty much every venom will have an effect of some kind on whatever tissue it comes into contact with, but the effects can vary greatly when it hits fatty tissue vs. muscle vs. a vein vs. mildly subcutaneous injections... Further, the different venom types evolved right along with the snake on both their digestion (venom is a digestive aid first and foremost) and the physical injection method. Elapids have fixed fangs, these are shorter than the moveable fangs of vipers and crotalids (sea snakes and mole vipers were only reccently reclassified, the same rules apply for fang length, prey type and venom type, but I'm going to address the larger groups where trends are more easily seen) and as such they are capable of subcutaneous injection but very rarely would they penetrate intramuscularly... The venom has a greater effect when injected in the manner that the snake itself would when striking and a greater effect on animals that they are likely to consume as prey items. Since only mice, rats and rabbits are used for LD tests (maybe chickens, but I've never seen results from this if it's been done) and only one injection method per test, the results are going to be skewed.

As an added problem, I have yet to see an LD test that tested every known venomous species, freshly milked and using each injection method... most test around a hundred species or so for one published set of results, usually with packaged and frozen venom (really, it takes an enormous amount of venom to perform these tests, multiple control groups of test subjects numbering several hundred each, multiple test groups used until that 50% mark is reached, then several repeated attempts of the results which produced the 50% and those measuremnts of venom similar to it... so if 0.05 mg produces the 50% fatality rate, 0.055, 0.054, 0.056, 0.053 all need to be repeatedly tested to verify the results) and usually with a single injection method that isn't representative of realistic envenomations.

Then the part that really gets me uppity when someone tries it in a friendly debate... LD tests are in no way indicative of the danger inherent in any given snake. I dislike the use of the term "danger" to start, these animals have a capability that needs to be respected, approached correctly, there is no "danger" just "controlled risk" but... in terms of practical application for danger or such meaningless terms as "most venomous" (seen on croc hunter... Irwin angers me frequently, I break a lot of remotes by throwing them at his fat head) the LD50s are useless. They fail to take into account the likelyhood of encountering the species, the likelyhood of an envenomation, the venom yeild and the ease of getting medical attention.

As an example... using the LD50 for subcutaneous injection, the tiger rattlesnake (Crotalus tigris) is far more toxic than the eastern diamondback rattlesnake (Crotalus adamanteus) Searching online for this information, as an easy way to verify it, http://www.kingsnake.com/toxinology/LD50/ld50iv.html contains a list with both species on it. The tiger has 0.56mg/kg needed to produce that 50% mortality rate in mice, the EDB has 1.65mg/kg to produce the same... Looking at the numbers as represented, the tiger seems far more dangerous, far more toxic... Until one realizes that the tiger has an average venom yeild of around 7-10 mg and the EDB has an average of 550-600mg (The potential is slightly higher or lower than the averages I listed, some sources will have a broader range, some narrower). Further, the EDB is a lot more likely to strike and a lot more likely to envenomate if handled/harassed.

Looking at specific record holders... The EDB has the highest venom yeild (to the best of my knowledge anyway) of any snake. The highest number of human fatalities would be African Saw Scaled vipers. The most toxic is up in the air for the various injection methods but usually results in either the inland taipan, the australian brown or one of several sea snakes. The highest number of deaths when represented as a percentage of envenomations is the golden lancehead (because medical attention was impossible to obtain for years, they're found on what amounts to a good sized rock in the middle of the ocean). The species usually listed as making handlers and zookeepers apprehensive or regarded as dangerous because of the animal's physical capabilities coupled with unpredicatability is most often the mambas (I've usually seen black, but a few sources have listed greens)...

So... after all that, the only thing I really said was that LD50s are only valuable as LD50s... if you want to know which species has the most toxic venom when injected in a certain manner into mice... then the LDs are the way to go. Any additional conclusions drawn from that information may or may not be correct, however logical them seem in casual reflection.